The present invention relates to a process and device for manufacturing an assembled cam shaft.
The auto engine is equipped with a suction valve to take the mixed gas into the cylinder and an exhaust valve to discharge the combustion gas out of the engine; and it is well-known that cam shafts are utilized to open and close these valves with appropriate timing. Conventional cam shafts have been castings but weight reduction of vehicle, improvement of production step of parts and cutdown of production cost are increasingly demanded in recent years. It is found, however, difficult to cast a hollow cam shaft with thin wall, to reduce the processing cost of each cam or journal, or to manufacture products of uniform quality. Moreover, virtually the limit has been reached in the qualitative improvement of materials for cam.
For these reasons, various processes for manufacturing assembled cam shafts by preparing a solid or hollow steel shaft and then assembling it with separately produced constituent parts such as cam, journal to make a cam shaft have been proposed in recent years. For the purpose of assembling the shaft to the constituent parts of a cam shaft, a mechanical forcing-in method, a method of hydraulically expanding a hollow shaft assembled with the parts, and so on have been so far conceived.
Cam pieces should be made of a specific abrasion-resistant material. In the case of the press-in method, if cam pieces are much harder than the shaft, the former, when forced in, will abrade the latter, rendering the method impracticable; and even if they can be forced in, the shaft diameter will change for every forcing, because a large number of them have to be forced in. In the case of the hydraulic expansion method, use of split molds is indispensable for setting the parts; and these parts, being made of a specific material characterized by abrasion-resistance and virtually zero elongation, are liable to be cracked by an increased internal pressure in time of expansion. Thus, either method has merits and demerits and its practical application is hardly realized.